I have a 99 F-150. Periodically, the service enging light will come on. The truck runs fine when this happens, although it does seem to idle faster and use more gas than when the light is not on. This tells me that some mechanism could be "sticking" or something like that. I can normally use some stp gas treatment and the light will go off after about 1/4 of a tank.

Can anyone tell me why this may be happening?

Thanks
rhenson

 

Go get your codes read so we can make informed guesses.

If you are in the USA except CA, go to AutoZone. They will read it for free. Otherwise, get your own reader or find someone who has one.

WRITE DOWN THE EXACT CODES. Come back here and post them for discussion. Do NOT let the drone at the parts counter sell you any parts unless he also happens to be an ASE certified mechanic.

Steve

 

The computer will keep the code even after the light goes out for so many startups after the light comes on. You can stop by Auto Zone or several other parts stores and have it read days or weeks later. They want to sell you the parts to repair, so they do the read for free. If they can't tell you what you need, post the code here and someone else may know the needed repair. Good luck!

 

I finally had a chance to get the codes read.

The only one that shows up is:
P1120 - Manufacturer Control. Fuel Air Metering

At first I was thinking air filter, but it's pretty new.

What do you guys think it might be??

Randy

 

I would start with the mass-airflow meter. If you have a shop manual and a volt-meter, you can easily check to see if it's bad.

I had one fail a while back, my truck lacked power, especially on long grades, and got bad MPG.

A remanufacturered one is only like $60 with core at AutoZone, but check to see if it's bad before you start replacing things.

 

A P1120 is a code on the Throttle Position Sensor out of range. I replaced mine while back easy to do. Part cost about 30.00 from Autozone. Wells makes the part and I compared the two and the factory installed one was the same as the Autozone part. Becareful when removing the old one. Some genius engineer put it on with phillips head screws and not very good ones. Just keep a good firm pressure on the screw and turn slow and hopefully you won't strip the head.

 

Thanks for the reply. Now can you tell me where I can see how to replace the part, and a part number?

Thanks again.

randy

 

Here is a link to a photo of a TPS.
https://www.f150online.com/forums/sh...ht=TPS+Install

The TPS is directly aross from your throttle linkage. It sits on the driver side on the throttle body. Remove screws pull straight out. When installing the new one there is a small arm on the sensor that fits in a slot that connects to the linkage arm. Turn the sensor with the connection pointing up then insert it and turn it down till the screw holes line up.

Autozone: Wells # TPS245

 

OK, so I got the TPS in today. Haven't gone out to actually find it on the truck yet, but I was wondering if once I install, is there any adjustments that have to be made? Or once I get it on there it should be good to go?

thanks
Randy

 

There may be minimal adjustment. If your Idle seems to high or low you can loosen the srews and move the sensor up or down depending on your idle. I had no problem with mine. Look where the screws are in location to the holes and when you put the new one on try to have them in the same location. Or you can use a multimeter to read the output of the sensor and adjust it that way. I think that link I showed you had the procedure for that. Just remember those screws will be alittle tight so be sure you have the proper size phillips screwdriver and take your time turning them out.

 

second to this, check the mass-air sensor as well. In Explorers, the design is famous for getting covered with crap and not working properly. A little alchol on a swab cleans it. I don't see why the F-150 couldn't also be affected by the same consition.

Do a search on the mass air sensor on instructions for locating (its just inside the intake) and cleaning.

 

Here is a list of things that should be done given the year of your truck:
Clean MAF Sensor, use a cleaner that wont leave a residue
Air Temp Sensor, Clean the same way as MAF, located in the intake tube also. Especially if you have a K&N or equivalent.
Clean EGR Ports with Throttle body cleaner
Clean Throttle body with same
Change Spark plugs, Use Motorcraft or Autolite Double Platnium
stay away from Bosch plugs and use plenty of dielectric grease.
Clean the IAC Valve located on the same elbow with the egr ports.
I have heard you could replace the boots on your coil over plugs but haven't checked into how much the boots are and if you could actually get them.
I have personnaly done everthing here and my truck runs like the day it was new and I have 80k on the odometer. I have also changed all the coil over plugs out. And changed the Throttle postion sensor and it gave me better throttle response after I did it. I will be changing the upstream O2 Sensors to see if I can gain any MPG back. Right now I'm getting about 14.5 Avg city/highway